The invention produces contactless radial position sensors having an equivalent angular aperture greater than 90°, and substantially eliminates the spurious microvibrations due to the imperfections of the current sensors. For this, the invention uses at least four independent sensors and an electronic device capable of virtually placing in series said sensors in groups of two or three in order to spread the equivalent angular aperture of said groups of sensors.
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1. A method of determining the radial position of a rotor relative to a stator, comprising the steps of:
measuring, by a first sensor, a first voltage linked to a position of a detection track relative to said first sensor;
measuring, by a second sensor, a second voltage linked to the position of the detection track relative to said second sensor;
measuring, by a third sensor, a third voltage linked to the position of the detection track relative to said third sensor;
measuring, by a fourth sensor, a fourth voltage linked to the position of the detection track relative to said fourth sensor;
calculating V3+V4−V1−V2 to determine the position of the detection track relative to the first actuation axis;
calculating V1+V4−V2−V3 to determine the position of the detection track relative to the second actuation axis,
wherein:
V1 is the first voltage;
V2 is the second voltage;
V3 is the third voltage;
V4 is the fourth voltage; and
the position of the detection track relative to the first and second actuation axes is an indication of the radial position of the rotor relative to the stator.
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The present application claims the benefit of French Patent Application No. 08 04478, filed Aug. 5, 2008, which is hereby incorporated by reference in its entirety.
The present invention relates to a device for measuring the radial position of a rotor relative to a stator in a wheel with magnetic bearings intended for space applications.
More specifically, the invention makes it possible to produce contactless radial position sensors having an equivalent angular aperture greater than 90°, and making it possible to eliminate as far as possible the spurious microvibrations due to the imperfections of the current measurement means, which will be explained hereinbelow.
These days, wheels with magnetic bearings intended for space applications in gyroscopic actuators comprise a rotor in levitation about a stator. This levitation is controlled by an electronic servo-control based on a position sensor, an actuator, conventionally a magnetic bearing, making it possible to provoke displacements of the rotor, and an electronic device which controls the actuator according to information given by the position sensor.
The position sensor concerned consists of a set of inductive sensors. It generally comprises a detection ring situated on the stator and a detection track situated on the rotor. The detection track is produced in a conductive material, generally a magnetic. The position sensor makes it possible to know the distance between the detection ring and the detection track.
However, the detection track, generally cylindrical, has defects which may be surface defects, or defects associated with the material itself: resistivity, particle size, etc. These defects cause spurious microvibrations of the rotor, because they are “seen” by the position sensor, and the electronic servo-control leads to multiple rotor displacement commands.
By definition, the defects of the detection track are periodic, since, on each revolution, a defect of the detection track passes once again in front of the same sensor. They can therefore be broken down into Fourier series comprising a fundamental component and harmonics of order 1 to N. The fundamental component is not a property of the detection track but rather a mechanical property of the complete magnetic bearing wheel device. It can be filtered in various ways.
The present invention applies to a context in which it is important to minimize the spurious microvibrations of the rotor.
The solutions that are currently envisaged fall into three categories: improving the detection track in order to minimize its defects; improving the sensor so that it does not “see” the defects of the detection track; filtering the defects using the electronics.
First of all, it is known by coupling two diametrically opposing sensors, the even order harmonics of the spurious vibrations can be eliminated. The position sensors of the state of the art can, for example, comprise four sensors coupled in pairs.
Furthermore, for the sensors to “see” a minimum of defects of the detection track, their angular aperture must be increased: thus, the state of the art has moved on from one-off sensors to sensors having an angular aperture close to 90°. These spread sensors “see” fewer defects, because they measure average values over a wide angle, which makes it possible to eliminate the high-order harmonics. However, too many spurious micro-vibrations remain; they correspond to the low-order harmonics of the Fourier series breakdown of the defects of the detection track.
The present invention provides a way of largely overcoming this persistent fault. Thus, to obtain a wheel with magnetic bearings subject to a minimum of spurious microvibrations, the invention proposes angularly spreading beyond 90° the aperture of the sensors, to a value making it possible to best smooth the defects of the detection track. This is made possible by the use of at least four electrically independent sensors offset relative to the actuation axes of the wheel with magnetic bearings.
To this end, the subject of the invention is a radial position sensing device intended for wheels with magnetic bearings, comprising:
Advantageously, the inventive device can comprise four sensors, of which a first sensor is offset by approximately 45° in the trigonometrical sense relative to the second actuation axis, and second, third and fourth sensors distributed uniformly in that order, at 90° to one another in the trigonometrical sense, in a plane defined by the first and second actuation axes of the direct orthogonal frame of reference.
Advantageously, each sensor has an angular aperture of between approximately 45° and 90°.
Advantageously, each sensor has an angular aperture of approximately 60°, making it possible to obtain, by coupling said sensors in pairs, an equivalent angular aperture of 120° per pair of sensors.
Advantageously, the inventive device can comprise six sensors, including a first sensor aligned with the second actuation axis and second, third,.fourth, fifth and sixth sensors distributed uniformly at 60° to one another in a plane defined by the first and second actuation axes of the direct orthogonal frame of reference.
Advantageously, each sensor has an angular aperture of between approximately 30° and 60°.
Advantageously, the inventive device also comprises an electronic device making it possible to electrically excite the sensors and perform computations based on the measurements performed by each of the sensors, making it possible to determine the position of the detection track relative to the detection ring in the direct orthogonal frame of reference.
Advantageously, a method of determining the radial position of a rotor relative to a stator comprises the use of the inventive device, and comprises the following steps.
Other features and benefits of the invention will become apparent from the following description, given in light of the appended drawings which represent:
As explained previously, these one-off sensors X1, X2, Y1, Y2 “see” defects of the detection track D1 which is not a perfect cylinder. Since the sensors X1, X2, Y1, Y2 are coupled in pairs of diametrically opposite sensors, only the even order harmonics of the Fourier series breakdown of the defects of the detection track D1 are cancelled out. The device thus perceives displacements of the rotor to be compensated and commands microdisplacements of the latter. This induces spurious microvibrations.
to the terminals of the sensor X1 and
to the terminals of the sensor X2. At the point Xp1, a voltage is measured which makes it possible to determine the position of the detection track D1 relative to the first actuation axis X.
However, microvibrations still persist and the object of the invention is to further reduce them.
The inventive device shown in
The six sensors Z1′, Z2′, Z3′, Z4′, Z5′, Z6′ are in this case also distributed uniformly, at 60° to one another. They can have an angular aperture ranging up to nearly 60°.
To sum up, the main benefit offered by the invention is that it makes it possible to cancel a large proportion of the spurious microvibrations that affect the current wheels with magnetic bearings. For this, the invention proposes to use at least four independent sensors and an electronic device capable of virtually placing in series said sensors in groups of two or three in order to spread to more than 90° the equivalent angular aperture of said groups of sensors.
Dargent, Thierry, Chassoulier, Damien, Champandard, Fabrice
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Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
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Aug 26 2009 | CHASSOULIER, DAMIEN | Thales | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 023181 | /0725 | |
Aug 26 2009 | CHAMPANDARD, FABRICE | Thales | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 023181 | /0725 | |
Aug 26 2009 | DARGENT, THIERRY | Thales | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 023181 | /0725 |
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